A head mounted display (HMD) refers to a digital device worn on the head of a user like glasses and configured to be provided with multimedia content. As digital devices are miniaturized, various wearable computers are being developed and the HMD is widely used. The HMD not only executes a simple display function but also provides various conveniences to users by being combined with augmented reality technology, N screen technology, etc.
The HMD can be used in connection with various external digital devices. The HMD can output content of an external digital device by communicating with the external digital device and receive user input for the external digital device or perform work in connection with the external digital device.